Regulations to limit the amount of volatile organic compound content (VOC) of industrial coatings has encouraged research and development projects directed at inventing new waterborne systems such as paints. With respect to the two most important commercial coating systems, polyesters and acrylics, it is a relatively easy task to characterize the current state-of-the-art: polymeric systems with a carbon backbone (acrylics) are more stable to hydrolysis then polyesters with their carbon-oxygen ester backbone chain. However, considerable research continues toward improving the stability of aqueous polyesters because of their inherently desirable properties of excellent hardness/flexibility ratios and outstanding gloss unattainable from aqueous acrylic systems.
U.S. Pat. No. 4,340,519 discloses the composition of certain crystalline and non crystalline polyesters copolymerized with a metal sulfonate group-containing aromatic acid and up to 10 mole percent (based on the total polyol content) of a polyvalent polyol selected from trimethylolpropane, trimethylolethane, glycerine, and pentaerythritol. Also, U.S. Pat. No. 4,525,524 discloses liquid systems comprised of polyester containing certain metal sulfonates and, optionally, up to 3 percent of a branching agent based upon the total diol component. Neither of these disclose the use of greater than 10 percent of branch inducing reactants.
U.S. Pat. No. 3,563,942 discloses linear solvent soluble copolyester compositions that can be dispersed in water. Water dispersibility is gained by the addition to the copolyester of a small amount (1-2 mole percent) of the metal salt of sulfonated aromatic compounds.
Many patents disclose methods to obtain water-dissipatable polyesters by neutralizing residual or unreacted carboxylic acid groups on the polymer with ammonia or various organic amines. U.S. Pat. No. 3,666,698 utilizes this method as well as phenylindandicarboxylic acid to modify coating performance. U.S. Pat. No. 3,699,066 shows the benefits of certain hydroxyfunctional amines for neutralization. U.S. Pat. No. 3,549,577 utilizes the aminoresin crosslinker as the neutralizing agent then adjusts the pH to prepare an alkaline water reduced system. In these patents as well as U.S. Pat. Nos. 3,494,882, 3,434,987, U.K. Pat. No. 1,117,126, and U.S. Pat. No. 3,345,313 carboxylic acid functionality is completely neutralized with excess base yielding an alkaline paint vehicle.
All of the U.S. patents and other references disclosed herein are incorporated herein by reference in their entirety.